fix: pocketbase healthcheck (add wget) + saveIfAbsent infinite recursion

- Add wget to pocketbase Alpine image so the docker-compose healthcheck
  (wget http://localhost:8090/api/health) can actually run
- Fix saveIfAbsent calling itself instead of app.Save(c) — was an
  infinite recursion that would stack-overflow on a fresh install

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/Dockerfile

@@ -48,7 +48,7 @@ ENTRYPOINT ["/backend"]
 # On every `serve` startup it applies any pending migrations automatically.
 # Data is stored in /pb_data (mounted as a Docker volume in production).
 FROM alpine:3.21 AS pocketbase
-RUN apk add --no-cache ca-certificates && \
+RUN apk add --no-cache ca-certificates wget && \
     addgroup -S appgroup && adduser -S appuser -G appgroup
 COPY --from=builder /out/pocketbase /pocketbase
 RUN mkdir -p /pb_data && chown appuser:appgroup /pb_data

backend/migrations/20260414000001_initial_schema.go

@@ -81,7 +81,7 @@ func saveIfAbsent(app core.App, c *core.Collection) error {
 	if _, err := app.FindCollectionByNameOrId(c.Name); err == nil {
 		return nil // already exists — skip
 	}
-	return saveIfAbsent(app, c)
+	return app.Save(c)
 }
 
 // ── Collection creators ───────────────────────────────────────────────────────